Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $241.96   11.578%   $269.9741   $269.97   $269.95   $270.00  
  Purchase #2 $60.93   3.401%   $63.0022   $63.00   $63.00   $63.00  
  Purchase #3 $23.65   12.186%   $26.532   $26.53   $26.55   $26.50  
  Purchase #4 $249.96   12.340%   $280.8051   $280.81   $280.80   $280.80  
  Purchase #5 $75.50   4.828%   $79.1451   $79.15   $79.15   $79.10  
  Purchase #6 $51.28   8.603%   $55.6916   $55.69   $55.70   $55.70  
  Purchase #7 $227.78   9.345%   $249.066   $249.07   $249.05   $249.10  
  7 purchase totals = $931.06       $1,024.2161   $1,024.22   $1,024.20   $1,024.20